1. Field of the Invention
The present invention relates to an antenna device preferably for use in a system such as a radio frequency identifier (RFID) system or a short-distance wireless communication system and to an electronic device including the antenna device.
2. Description of the Related Art
An antenna device used in a RFID card reader/writer is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-298095.
When a coil antenna approaches a metal plate, eddy currents usually occur in the metal plate and adversely affect the characteristics of the coil antenna. To address such an effect, a typical antenna device includes a magnetic sheet interposed between the coil antenna and the metal plate, as illustrated in Japanese Unexamined Patent Application Publication No. 2002-298095.
In the antenna device disclosed in Japanese Unexamined Patent Application Publication No. 2002-298095, the magnetic body shields the magnetic field of the coil antenna, so that eddy currents are prevented from occurring in the metal plate. Thus, the antenna device is capable of communicating with a communication counterpart antenna when the communication counterpart antenna is located on the side of the antenna device on which the coil antenna is located.
However, since the magnetic body and the metal plate shield the magnetic field of the coil antenna, the antenna device is not capable of communicating with a communication counterpart antenna when the communication counterpart antenna is located on the metal-plate side of the antenna device.